Which statement best describes the effect of 2,3-BPG on the oxygen dissociation curve?

Which statement best describes the effect of 2,3-BPG on the oxygen dissociation curve?

• A. It shifts left, increasing Hb affinity and reducing unloading.
• B. It increases Hb concentration.
• C. It shifts to the right, facilitating O2 unloading.
• D. It reduces Hb's capacity to carry O2.

Answer: (C)

The main idea is how 2,3-BPG changes hemoglobin’s oxygen affinity. 2,3-BPG binds to deoxyhemoglobin and stabilizes the T (taut) state, which lowers hemoglobin’s affinity for oxygen. Because of this, the oxygen dissociation curve shifts to the right. A rightward shift means hemoglobin releases oxygen more readily to tissues at any given partial pressure of oxygen, improving unloading where it’s needed. This adjustment helps deliver more O2 under conditions that raise 2,3-BPG, such as chronic hypoxia or high altitude. It doesn’t increase the amount of hemoglobin available, nor does it reduce the total capacity to carry O2; it changes how readily O2 is released.